This invention pertains to a portland cement concrete mixture that provides increased durability in the hardened state of such a mixture within freeze/thaw temperature cycles under conditions of water saturation. The mixture may include concrete materials in combination with cement additive compositions such as water reducing admixtures, air entraining agents and plasticizers.
The development of portland cement dates back to 1824. An early disclosure is contained in British Patent No. 5022, for "An Improvement in the Modes of Producing an Artificial Stone," to Joseph Aspdin. Conventional portland cement is described in the American Society for Testing and Materials ("ASTM") Standard C150-89, "Standard Specification for Portland Cement," which is incorporated herein by reference.
Portland cement may be blended with a variety of coarse aggregates such as crushed limestone or gravel as well as a fine aggregate. The proportions of portland cement and fine aggregate may be varied depending upon the properties and the use of the concrete. Conventional aggregates for use in concrete are described in the requirements of the American Society for Testing and Materials ("ASTM") Standard C33-90, "Standard Specification for Concrete Aggregates," which is incorporated herein by reference.
In the past, coarse aggregates have fallen within the broad range of 2 inches (7.6 cm) to 3/8 inch mesh; the size of the fine aggregate has been in a broad range of about a No. 4 mesh to a No. 200 mesh pursuant to ASTM C-11 standard sieve specification. Coarse aggregates of mineral origin, such as gravel or crushed limestone, have been used. A manufactured aggregate such as slag has also been used.
Portland cement concrete may also incorporate a pozzolanic material such as a man-made type pozzolan such as fly ash, being produced from the burning of coal. Granulated ground slag from the blast furnace slag material from the steel industry has also been used, or silica fume from the silicon and ferosilicon industry. Natural pozzolan which comes from certain pumieties of natural volcanic origin has also been employed. The most widely used pozzolanic material, however, is the type C fly ash derived from the burning of coal in the power plants that provide electricity.
Chemical admixtures have also been incorporated into portland cement concrete. The chemical admixtures used in portland cement concrete have included water reducing admixtures such as calcium lignosulfonate. Concrete containing hydraulic cement and a water soluble derivative of lignin is disclosed in U.S. Pat. No. 2,141,570, to J. G. Mark, for "Concrete and Hydraulic Cement" A cement mix containing waste sulphite liquor is disclosed in U.S. Pat. No. 2,169,980, to E. W. Scripture, for "Cement Mix." Hydroxyalkyl amines, such as triethanolamine, have been incorporated into calcium lignosulfonate as an accelerator to counteract the set retardation caused by the dispersant. An example of a disclosure of an amine salt is contained in U.S. Pat. No. 2,052,586, to G. R. Tucker, for "Amine Salts of Aromatic Sulfonic Acids." Additional information relating to chemical admixtures to be added to portland cement concrete mixtures for various purposes is disclosed in ASTM C494-90, "Standard Specification for Chemical Admixtures for Concrete," which is incorporated herein by reference.
Various other accelerators have been used to offset the retardation of calcium lignosulfonate, ammonium lignosulfonate or sodium lignosulfonate. These accelerators include calcium chloride, nitrite, nitrate, formate and thiocyanate salts of the alkali and alkaline earth metals. U.S. Pat. No. 4,373,956, to Rosskopf, discloses a cement mixture comprising an alkali or alkaline earth or ammonium salt of thiocyanic acid in combination with an alkanolamine. Such a combination of ingredients has been added to a cementitious mix in an effort to increase the rate of hardening of the mix and to increase the compressive strength of the mix after hardening. Furthermore, U.S. Pat. No. 4,473,405, to Gerber, discloses a mixture including a combination of alkali or alkaline earth metal nitrates, alkanolamines and alkali or alkaline earth metal thiocyanates. Other formulations of water reducing admixtures that were manufactured to increase the water reduction and compressive strength of portland cement concrete have been used in the past. Other accelerators used in the past include carbohydrates such as glucose and corn syrup, and gluconates such as gluconic acid and heptogluconic acids.
Air entrainment which forms a system of air bubbles that will remain in the mix after concrete hardening has an important effect upon the durability of concrete in freeze/thaw temperature cycles. The use of a surface active agent or surfactants is generally necessary to obtain satisfactory amounts of air entrainment. A number of chemical agents have been employed to achieve satisfactory amounts of air entraiment. Generally, the chemical agents are organic chemicals that are broadly classified as soaps and detergents. One example of a chemical agent of this type is neutralized Vinsol resin, manufactured by Hercules, Inc. in Wilmington, Del. Vinsol resin is composed of alkali salts of pinewood resin extracts. A test method for materials used as air-entraining admixtures is disclosed in ASTM C233-90, "Standard Test Method for Air-Entraining Admixtures for Concrete," which is incorporated herein by reference.
In the past, a variety of surfactants has been used, both ionic and non-ionic, in a broad class of detergents to obtain the desired degree of air entrainment. In concrete, for example, U.S. Pat. No. 4,249,948, to Okada et al., discloses the use of an alpha-olefin acid salt, which is said to act as an air entraining agent in the portland cement concrete mix in an effort to improve freeze/thaw resistance. U.S. Pat. No. 4,689,083, to Gutmann et al., discloses a portland cement mix containing an air entraining additive consisting essentially of a coconut fatty acid diethanolamine. The coconut fatty acid diethanolamine is produced by reacting an alkyl ester of coconut acid with diethanolamine, whereby air will be entrained in the mix in the amount of 3% to 9% by volume of the mix.
Experience with conventional concrete admixtures' resistance to repetitive freeze/thaw temperature cycles has not been completely satisfactory. Scaling attributable to improper air void systems, pop-outs due to shale and chert particles in both the limestone and gravel fraction of the coarse aggregate, and shale in the gravel and sand fractions of the portland cement concrete have resulted. Problems associated with the phenomena of surface deterioration have not been solved. The need remains for a portland cement concrete mix that would be more durable when subjected to freeze/thaw temperature cycles.
When a mix is harsh and difficult to finish properly, excessive finishing, water spraying and other means are sometimes employed to bring paste to the top,, causing a weak surface. This may contribute to deterioration of the concrete in freeze/thaw conditions. Such weakness can only be corrected through proper mix designs and the use of chemicals and plasticizers, in accordance with the present invention.